It all depends...

Sometimes, the job will spec a seperate ground wire. By code, EMT is permitted as the grounding path, and a ground wire does not have to be run in EMT. (Sorry, i dont have the book in front of me, so i cant tell you the section.) Usually, a seperate ground wire is run for an added measure of safety.

BX is rarely used anymore, and it does not contain a ground wire anyway.

A receptacle must always be bonded to a metal box, unless it is a self-grounding receptacle. if a ground wire is run, it must be bonded to the box and the receptacle, again, unless it is a self-grounding recetacle. (the ground wire still must be bonded to the box in this case)

Wire gauges are as follows:
15 amp=#14
20 amp=#12
30 amp=#10

The grounding jumper must always be the same size as the circuit conductors.

I don't believe it is allowed to recode a white wire green the way you described. if you are using AC (BX), the metal sheath serves as the ground, so I don't see why you would need to use the white wire as the ground anyway. [Linked Image] All you would have to do is bond the receptacle to the box, and it would be grounded.

Peter